The present invention relates to an improvement of all optical device for forming a magnified image of an object onto a light receiving surface, and more specifically, to the optical device which is employed in an imaging apparatus such as a copy machine which is capable of varying its magnifying power.
Conventionally, in this kind of optical device, a zoom lens system is mounted on a carriage. The carriage is engaged with a driving unit which is mounted on a base plate provided on an apparatus main body for shifting the carriage in a direction along the optical axis of the zoom lens system. Further, a guide shaft is arranged in parallel with the optical axis of the zoom lens system in order for guiding the carriage. Pulleys and a wire are interposed between the carriage and the carriage driving unit so that the carriage is smoothly shifted in the direction along the optical axis of the zoom lens system in accordance with the actuation of the driving unit.
The zoom lens system includes a variable power lens group and a correction lens group. The variable lens group can be shifted in the direction along the optical axis thereof by means of a cam mechanism so as to change its magnification synchronously with the movement of the carriage.
It should be noted that in this kind of conventional optical device, a manufacturing error of an individual lens or an overall installation error of an apparatus could not be easily corrected, since all of the shift movements of the variable power lens group and the correction lens group were mechanically performed by a cam mechanism.
For example, a manufacturing error of lenses may cause small optical property differences such as an error of a focal distance or a color aberration. In such a case, in order to eliminate an effect of this kind of manufacturing error, it was required to change a cam configuration in each apparatus. Such a measure costs too much to introduce into a practice for mass-production.